Tyre carcass forming method and drum

ABSTRACT

To form a tyre carcass, a body ply is wound about a drum, which has two half-drums movable axially in opposite directions to and from a centre plane of the drum, and having respective turn-up bladders, on each of which is laid a respective annular lateral portion of the body ply; each annular lateral portion being turned up about a respective bead bundle and onto a sidewall of a toroidal-shaped annular central portion of the body ply by inflating the relative turn-up bladder and controlling distension of a given annular portion of the turn-up bladder so that, when inflation is completed, the annular portion assumes a given final position, in which an intermediate portion of the turn-up bladder rolls outwards along the relative sidewall of the annular central portion of the body ply.

TECHNICAL FIELD

The present invention relates to a tyre carcass forming method and drum.

More specifically, the present invention relates to an improvement to aknown forming method, which employs a drum comprising two half-drumsmovable axially in opposite directions to and from a central plane ofthe drum, and comprising respective turn-up bladders.

BACKGROUND ART

In this known method, a tyre carcass is formed by:

-   -   winding a body ply about the drum, so that two annular lateral        portions of the body ply rest on the respective turn-up        bladders;    -   fitting a respective bead bundle on each half-drum and        respective annular lateral portion;    -   clamping the bead bundles in position on the drum; the beads        defining, on the body ply, the two annular lateral portions        outwards of the bead bundles, and a central portion between the        bead bundles;    -   moving the two half-drums towards each other to form the central        portion into a toroidal shape; and    -   once the central portion is shaped, applying air inflation        pressure to expand the annular lateral portions outwards and        about the respective bead bundles.

In the above known tyre carcass forming method, simply inflating theturn-up bladders is rarely sufficient, especially in the case ofextensive turn-ups, to ensure firm adhesion of the turned-up annularlateral portions to the respective sidewalls of the toroidal centralportion.

Consequently, each turn-up bladder is known to be associated with atleast one respective push bladder located axially outwards of therelative turn-up bladder, and which, when inflated, presses the relativeturn-up bladder against the relative sidewall of the central portion ofthe body ply. When so pressed, the turn-up bladder expands radiallyoutwards to increase the portion of its outer surface adhering to therelative sidewall of the central portion, and so complete turn-up of therelative annular lateral portion of the body ply.

Using push bladders poses several drawbacks, on account of each turn-upbladder being expanded radially by the relative push bladder subjectingit to severe axial thrust, which, for an average-size tyre carcass, isin the region of a few tons, and is transmitted to the toroidal centralportion of the body ply.

Bearing in mind that:

-   -   the carcass is green;    -   the axial thrust exerted by the push bladders can only be        counteracted by feeding compressed air into the toroidal central        portion of the body ply; and    -   the greater the air pressure inside the central portion, the        greater the problems posed in terms of airtightness and        structural resistance of the central portion;        the only way of counteracting the axial thrust of the push        bladders, in the case of relatively high turn-ups, is to inflate        a central bladder inside the toroidal central portion, which        involves added cost and equally serious structural problems.

In addition to structural problems, push bladders also pose sizeproblems, by being located at least partly outwards of the relativeturn-up bladders on the half-drums. As a result, the half-drums must bebuilt long enough to support the relative push bladders, which means anincrease in size, stronger drum supporting structures as a whole, andconsiderable added cost.

The above considerations apply even more so when, as in U.S. Pat. No.5,660,677 and U.S. Pat. No. 2,986,196, the push bladders are replaced byexternal hydraulically or pneumatically operated push devices. In whichcase, the external push devices not only greatly increase the axial sizeof the drum, but also make it substantially impossible to employ thedrum on multidrum turrets commonly used in the tyre industry. Moreover,unlike push bladders, which subject the turn-up bladders tosubstantially evenly distributed stress, external push devices—normallycomprising push cans—subject the turn-up bladders to more or lessconcentrated stress that greatly reduces the working life of the turn-upbladders.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a tyre carcassforming method that is cheap and easy to implement, while at the sametime eliminating the aforementioned drawbacks.

According to the present invention, there is provided a tyre carcassforming method as claimed in Claim 1 and preferably in any one of thefollowing Claims depending directly or indirectly on Claim 1.

The present invention also relates to a tyre carcass forming drum.

According to the present invention, there is provided a tyre carcassforming drum as claimed in Claim 22 and preferably in any one of thefollowing Claims depending directly or indirectly on Claim 22.

BRIEF DESCRIPTION OF THE DRAWINGS

A number of non-limiting embodiments of the present invention will bedescribed by way of example with reference to the accompanying drawings,in which:

FIG. 1 shows a schematic partial axial and radial section of a firstpreferred embodiment of the drum according to the present invention;

FIGS. 2 to 4 are similar to FIG. 1, and show the FIG. 1 drum inrespective different operating positions;

FIG. 5 shows a schematic view in perspective of a detail in FIG. 4;

FIGS. 6 and 7 are similar to FIGS. 2 and 4 respectively, and show afirst variation of the drum in FIGS. 1 to 4;

FIG. 8 is similar to FIG. 7, and shows a second variation of the drum inFIGS. 1 to 5.

BEST MODE FOR CARRYING OUT THE INVENTION

Number 1 in FIGS. 1 to 4 indicates as a whole a drum for forming avehicle tyre carcass 2 (FIG. 4).

Drum 1 has a longitudinal axis 3 and a centre plane 4 perpendicular tolongitudinal axis 3, and comprises two rigid half-drums 5 (only oneshown) of fixed axial length, which are positioned specularly withrespect to centre plane 4, are coaxial with longitudinal axis 3, and aremovable axially in opposite directions to and from centre plane 4 by aknown powered screw-nut screw transmission not shown.

Each half-drum 5 is fitted, at the end facing centre plane 4, with arespective known clamping device 6 for clamping a respective bead bundle7, and supports a respective annular turn-up bladder 8, which lies, atrest, along half-drum 5, and has an inner annular fastening shoe 9housed inside a respective annular groove 10 formed in a cylindricalouter surface 11 of half-drum 5, adjacent to clamping device 6. At theopposite end to inner annular fastening shoe 9, turn-up bladder 8 has anannular portion defining an outer annular fastening shoe 12, which, atrest, rests on outer surface 11.

Each half-drum 5 comprises an elastic tubular membrane 13, which, atrest (FIG. 1), rests on outer surface 11 of half-drum 5 and beneathturn-up bladder 8, has an annular fastening shoe 14 housed inside anannular groove 15 formed in cylindrical outer surface 11 of half-drum 5,adjacent to the free end of half-drum 5, and terminates, at the oppositeend to fastening shoe 14, with an end portion 16 located close toannular groove 10 and connected integrally to outer fastening shoe 12 ofturn-up bladder 8.

As shown more clearly in FIG. 5, tubular membrane 13 decreases inthickness from fastening shoe 14, and is fitted inside with axialstiffeners 17 preferably defined by metal wires.

As shown more clearly in FIG. 4, each turn-up bladder 8 and relativetubular membrane 13 define, about outer surface 11 of relative half-drum5, a single annular chamber 18, to which air inflation pressure can beapplied by inflating it with compressed air by means of a knownpneumatic circuit (not shown) communicating with annular chamber 18 viaa conduit 19 extending through relative half-drum 5.

In actual use, a body ply 20 is wound about drum 1 in the rest positionshown in FIG. 1, in which the two half-drums 5 are a maximum distanceapart, and turn-up bladders 8 are fully deflated and rest on the outersurface of respective tubular membranes 13, which rest on outer surface11 of relative half-drums 5.

In this position, body ply 20 rests on each clamping device 6 with theinterposition of a respective annular strip 21 defined by a lateralannular appendix of relative turn-up bladder 8, for the purposeexplained below.

In this position, clamping devices 6 define, on body ply 20, an annularcentral portion 22 between the two clamping devices 6; and two annularlateral portions 23, each extending outwards of relative clamping device6 and surrounding relative turn-up bladder 8.

Obviously, body ply 20 is not applied directly contacting drum 1, whichis fitted first with other component parts not shown for the sake ofsimplicity, and which normally comprise a composite layer defined by acentral innerliner, two lateral abrasion strips, and two outer sidewallstrips.

A respective bead bundle 7 is then fitted to annular lateral portion 23on each half-drum 5, and is clamped in position by expanding relativeclamping device 6 in known manner (FIG. 2). At this point, compressedair is fed in known manner underneath annular central portion 22, and,at the same time, the two half-drums are moved towards each other andcentral plane 4 (FIG. 2) to form annular central portion 22 into atoroidal shape with two annular sidewalls 24 substantially perpendicularto longitudinal axis 3.

At this point, compressed air is fed along conduits into annularchambers 18. As shown clearly in the drawings, turn-up bladders 8 beingmuch more deformable than relative tubular membranes 13, the compressedair fed into annular chambers 18 first expands turn-up bladders 8 (FIG.3) to partly fold annular lateral portions 23 outwards and aboutrelative bead bundles 7, and then gradually flares tubular membranes 13(FIG. 4), the end portion 16 of each of which is gradually distended byair inflation pressure only, thus gradually distending and raising outerfastening shoe 12 of the relative turn-up bladder substantiallyradially.

In connection with the above, it should be pointed out that, as eachturn-up bladder 8 is distended, the relative tubular membrane 13, beingaxially rigid, acts as a conical brace to prevent substantially axialmovement, and only permit substantially radial movement, of any point Palong relative outer fastening shoe 12. More specifically, as turn-upbladder 8 is distended, the conical brace defined by relative tubularmembrane 13 guides each point P along a substantially circulartrajectory T, which is perpendicular to outer surface 11 of half-drum 5at the point of intersection with outer surface 11, and extends in aradial plane through longitudinal axis 3 and point P, and about arespective centre C located at relative fastening shoe 14.

In other words, as each turn-up bladder 8 is distended, relative tubularmembrane 13 forces a given annular portion of turn-up bladder 8—in theexample shown, outer fastening shoe 12—to move substantially radiallybetween a rest position on outer surface 11 of half-drum 5, and a givendistended position coaxial with longitudinal axis 3.

Comparison of the FIGS. 3 and 4 configurations shows that, for eachturn-up bladder 8:

-   -   annular strip 21 performs the dual function of preventing        compressed-air leakage from the chamber defined by toroidal        annular central portion 22, and ensuring the expanding turn-up        bladder 8 is kept as firmly as possible in contact with relative        sidewall 24;    -   radial distension of outer fastening shoe 12 pushes the whole of        turn-up bladder 8 outwards towards relative sidewall 24;    -   as a result, a central portion of turn-up bladder 8 rolls        gradually along sidewall 24 to gradually turn annular lateral        portion 23 of body ply 20 up onto sidewall 24;    -   by virtue of the central portion of turn-up bladder 8 rolling,        together with annular lateral portion 23, on sidewall 24,        annular lateral portion 23 gradually adheres to sidewall 24 with        no sliding movement between annular lateral portion 23 and        turn-up bladder 8, on one side, and sidewall 24 on the other;        and    -   annular lateral portion 23 is gradually turned up completely        onto sidewall 24 without subjecting toroidal annular central        portion 22 to any additional axial stress, over and above that        applied by expansion of turn-up bladder 8.

In the FIG. 1-5 embodiment, tubular membrane 13 decreases in thicknesstowards the centre plane, so that it flexes in much the same way as aleaf spring. However, a tubular membrane 13 of constant thickness (notshown), reinforced axially to brace and guide outer fastening shoe 12,is obviously also perfectly acceptable.

In the FIGS. 6 and 7 variation, to ensure even, balanced deformation ofouter fastening shoes 12, i.e. to ensure each tubular membrane 13 flarescoaxially with longitudinal axis 3, each annular chamber 18 is dividedinto two annular chambers 25 and 26, communicating with respective feedconduits 27 and 28, by a respective radial push bladder 29, which, whenexpanded (FIG. 7), has a section substantially in the form of anisosceles triangle with its apex facing the free end of half-drum 5, aradially inner side 30 contacting outer surface 11 of half-drum 5, and aradially cuter side 31 covered with tubular membrane 13 and supportingouter fastening shoe 12 of turn-up bladder 8 at the end facing centreplane 4. Radial push bladder 29 is connected to half-drum 5 by twofastening shoes 32 and 33 connected to the outer ends of respectivesides 30, 31, and housed in respective annular grooves formed inhalf-drum 5, on opposite sides of conduit 27.

The FIG. 8 variation is similar to the FIG. 1-5 embodiment, except thateach half-drum 5 only supports a turn-up bladder 34 comprising a portion35 corresponding in shape and size to a turn-up bladder 8, and securedto half-drum 5 by an inner fastening shoe 36 corresponding to an innerfastening shoe 9; and a further portion 37, which, at one end, has aninner annular end portion 38 integral with an outer end portion ofportion 35, and is secured to half-drum 5, at the other end, by an outerfastening shoe 39 corresponding to a fastening shoe 14. Portion 37 isreinforced with longitudinal ribs 40, which are fitted integrally to theouter surface of portion 37, extend the whole length of portion 37, andprovide for bracing and guiding each point P of inner annular endportion 38 along trajectory T and about centre C as described withreference to the FIG. 1-5 embodiment.

The FIG. 8 variation performs in the same way as the FIG. 1-5embodiment, and so requires no further explanation.

1) A method of forming a tyre carcass, the method comprising the stepsof: preparing a drum having a longitudinal axis and comprising twohalf-drums of fixed axial length, which are movable, in oppositedirections along the longitudinal axis, to and from a centre plane ofthe drum, and are covered externally with respective turn-up bladders;winding a body ply about the drum, so that two annular lateral portionsof the body ply lie on at least part of the relative turn-up bladders;fitting a respective bead bundle on each half-drum and relative annularlateral portion; each annular lateral portion extending outwards of therelative bead bundle; clamping each bead bundle in position on therelative half-drum; forming an annular central portion, extendingbetween the two bead bundles, of the body ply into a toroidal shape bymoving the two half-drums towards each other; and once the annularcentral portion is shaped, applying air inflation pressure to expand theannular lateral portions outwards and up about the relative beadbundles; the method comprising the further steps of: distending, on eachhalf-drum and by applying said air inflation pressure, a given annularportion of the relative turn up bladder; and controlling distension ofsaid annular portion using guide means, which are axially fixed withrespect to the half-drum, are rigid with said annular portion andrespond solely to application of said air inflation pressure; and insuch a manner as to move said annular portion into a final position, andto cause an intermediate portion, extending between said annular portionand the toroidal said annular central portion, of the turn-up bladder toroll outwards along a relative sidewall of the toroidal annular centralportion. 2) A method as claimed in claim 1, wherein said final positionof said annular portion is a position coaxial with said longitudinalaxis. 3) A method as claimed in claim 1, wherein the guide means controlthe relative annular portion so that each point of the annular portiontravels along a respective given fixed trajectory in relation to therelevant half-drum. 4) A method as claimed in claim 3, wherein saidtrajectory of each point of the annular portion is a substantiallyradial trajectory with respect to the longitudinal axis. 5) A method asclaimed in claim 3, wherein said trajectory of each point of the annularportion is a circular trajectory in a radial plane through saidlongitudinal axis and said point. 6) A method as claimed in claim 5,wherein the circular trajectory of each point of the annular portionextends about a centre lying in the relative said radial plane, outsidethe relative turn-up bladder, and on an outer surface of the relativehalf-drum. 7) A method as claimed in claim 1, wherein the guide meansare bracing means. 8) A method as claimed in claim 1, wherein eachturn-up bladder has an inner annular shoe secured in a fixed position tothe relative half-drum; and an outer annular shoe defining the relativesaid annular portion. 9) A method as claimed in claim 8, wherein saidguide means comprise, for each half-drum, a tubular membrane, which isfitted in an axially fixed position to the relative half-drum, and iselastically deformable radially, but axially substantially rigid; an endportion, facing the centre plane, of the tubular membrane being fittedwith said outer annular shoe of the relative turn-up bladder; and theouter annular shoe being distended into said given final position byflaring the tubular membrane by application of said air inflationpressure. 10) A method as claimed in claim 9, wherein the tubularmembrane varies in thickness longitudinally. 11) A method as claimed inclaim 9, wherein the tubular membrane decreases in thickness towards thecentre plane. 12) A method as claimed in claim 9, wherein the tubularmembrane comprises axial stiffeners. 13) A method as claimed in claim 9,wherein the tubular membrane defines, with the relative turn-up bladder,a single annular chamber, to which said air inflation pressure isapplied by a single compressed-air feed means. 14) A method as claimedin claim 13, wherein, at the opposite end to that facing the centreplane, the tubular membrane comprises a respective fastening shoe forattachment to the relative half-drum. 15) A method as claimed in claim1, wherein each turn-up bladder comprises an inner shoe and an outershoe fitted to the opposite ends of the relative half-drum; a firstportion adjacent to the inner shoe; and a second portion adjacent to theouter shoe; said guide means being located on the second portion; andsaid annular portion being an end portion for attaching the secondportion to the first portion. 16) A method as claimed in claim 15,wherein the guide means are means for axially stiffening the secondportion. 17) A method as claimed in claim 15, wherein the guide meanscomprise, for each turn-up bladder, a number of ribs secured axially tothe relative second portion. 18) A method as claimed in claim 7, whereinsaid outer annular shoe is distended by applying the air inflationpressure to a radial push bladder associated with the relative turn-upbladder and located on the opposite side of the turn-up bladder to thecentre plane; the push bladder supporting the outer annular shoe of therelative turn-up bladder, and the relative said guide means. 19) Amethod as claimed in claim 18, wherein the radial push bladder, whenexpanded, has a substantially triangular section; a radially inner firstside of the push bladder being positioned contacting an outer surface ofthe relative half-drum; and a radially outer second side of the pushbladder supporting said guide means and the outer annular shoe of therelative turn-up bladder. 20) A method as claimed in claim 18, wherein,on each half-drum, the air inflation pressure is applied simultaneouslyto the push bladder and the turn-up bladder by injecting compressed airby means of a first and second feed means respectively. 21) A method asclaimed in claim 20, wherein the push bladder comprises two shoes fordirect connection to the relative half-drum; said two shoes beinglocated side by side, close to a free end of the relative half-drum, andon opposite sides of the first feed means. 22) A drum for forming a tyrecarcass, the drum having a longitudinal axis, and comprising twohalf-drums of fixed axial length, which are movable in oppositedirections along the longitudinal axis to and from a centre plane of thedrum, and have respective turn-up bladders, each of which has at least afirst annular shoe connected directly to the relative half-drum; andpneumatic inflation means for distending a given annular portion of eachturn-up bladder; the drum comprising, on each half-drum, guide means,which are axially fixed with respect to the half-drum, are rigid withsaid annular portion and are activated by the pneumatic inflation meansto move the annular portion into a given final position. 23) A drum asclaimed in claim 22, wherein said final position of said annular portionis a position coaxial with said longitudinal axis. 24) A drum as claimedin claim 22, wherein the guide means guide each point of the annularportion along a respective fixed trajectory in relation to the relevanthalf-drum as the annular portion is distended between an undeformedinitial position and said final position. 25) A drum as claimed in claim24, wherein said trajectory is a substantially radial trajectory withrespect to the longitudinal axis. 26) A drum as claimed in claim 24,wherein said trajectory is a circular trajectory in a radial planethrough the longitudinal axis and said point. 27) A drum as claimed inclaim 26, wherein the circular trajectory of each point of the annularportion extends about a centre lying in the relative said radial plane,outside the relative turn-up bladder, and on an outer surface of therelative half-drum. 28) A drum as claimed in claim 22, wherein the guidemeans are bracing means. 29) A drum as claimed in claim 22, wherein eachturn-up bladder has a second annular shoe defining the relative saidannular portion. 30) A drum as claimed in claim 29, wherein the guidemeans comprise, for each half-drum, a tubular membrane, which is fittedin an axially fixed position to the relative half-drum, and iselastically deformable radially, but axially substantially rigid; an endportion, facing the centre plane, of the tubular membrane being fittedwith the second annular shoe of the relative turn-up bladder. 31) A drumas claimed in claim 30, wherein the tubular membrane varies in thicknesslongitudinally. 32) A drum as claimed in claim 30, wherein the tubularmembrane decreases in thickness towards the centre plane. 33) A drum asclaimed in claim 30, wherein the tubular membrane comprises axialstiffeners. 34) A drum as claimed in claim 30, wherein the tubularmembrane defines, with the relative turn-up bladder, a single annularchamber; the pneumatic inflation means comprising a singlecompressed-air feed means communicating with said annular chamber andfor applying the air inflation pressure. 35) A drum as claimed in claim34, wherein, at the opposite end to that facing the centre plane, thetubular membrane comprises a respective fastening shoe for attachment tothe relative half-drum. 36) A drum as claimed in claim 22, wherein eachturn-up bladder comprises a first and a second annular shoe fitted tothe opposite ends of the relative half-drum; a first portion adjacent tothe first annular shoe; and a second portion adjacent to the secondannular shoe; the guide means being located on the second portion; andsaid annular portion being an end portion for attaching the secondportion to the first portion. 37) A drum as claimed in claim 36, whereinthe guide means are means for axially stiffening the second portion. 38)A drum as claimed in claim 35, wherein the guide means comprise, foreach turn-up bladder, a number of ribs secured axially to the relativesecond portion. 39) A drum as claimed in claim 29, and comprising, foreach turn-up bladder, a radial push bladder located on the opposite sideof the turn-up bladder to the centre plane; each radial push bladdersupporting the second annular shoe of the relative turn-up bladder, andthe relative said guide means, and communicating with said pneumaticinflation means. 40) A drum as claimed in claim 39, wherein the radialpush bladder, when expanded, has a substantially triangular section; aradially inner first side of the radial push bladder being positionedcontacting an outer surface of the relative half-drum; and a radiallyouter second side of the radial push bladder supporting the guide meansand the second annular shoe of the relative turn-up bladder. 41) A drumas claimed in claim 39, wherein, on each half-drum, said pneumaticinflation means comprise a first and a second feed means for feedingcompressed air to the radial push bladder and the turn-up bladderrespectively. 42) A drum as claimed in claim 41, wherein the radial pushbladder comprises two shoes for direct connection to the relativehalf-drum; said two shoes being located side by side, close to a freeend of the relative half-drum, and on opposite sides of the first feedmeans.